Project Summary/Abstract Insulin levels are inadequate to maintain euglycemia in patients with type-2 diabetes mellitus (T2DM) and in animal models of the disease, which is due in part to ?-cell dysfunction. While perturbations of ?-cell cation levels result in aberrant function, the identity and role(s) of the ion channels that contribute to defective ?-cell cation homeostasis during the pathogenesis of T2DM remain largely unknown. This is an important problem because, without this knowledge, our understanding of ?-cell dysfunction in T2DM is incomplete, which limits the targets that can be utilized for treating diabetes. The mucolipin subfamily of the transient receptor cation channels (TRPM) are key regulators of ?-cell function. The most abundant pancreatic islet TRPM channel, TRPM7 is essential for maintaining cellular Mg2+ homeostasis. The long term goal of this research is to under- stand physiological and pathophysiological ?-cell function in the context of TRPM7 channels. The overall ob- jective of this proposal is to elucidate the influence of pancreatic ?-cell TPRM7 channels on function and de- velopment. This project will test the central hypothesis that TRPM7 channel modulation of Mg2+ homeostasis controls ?-cell mass and function. This hypothesis has been formulated from preliminary data that finds that TRPM7 regulates ?-cell development, proliferation, Mg2+ content, Ca2+ influx and glucose-stimulated insulin secretion (GSIS). The rationale for the proposed project is that understanding how Mg2+ homeostasis is modu- lated by TRPM7 channel activity will expose new therapeutic targets aimed at improving approaches for gen- erating ?-cells from pluripotent cell sources for the treatment of T2DM. Guided by strong preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) Determine how TRPM7 regulates pancreatic ?-cell development; and 2) Determine how TRPM7 modulates adult ?-cell function. Under the first aim, mice with to- tal pancreatic, total endocrine, or ?-cell specific ablation of TRPM7, which are already on hand, will be utilized to test how this channel regulates ?-cell development. This aim will also determine how TRPM7 activity modu- lates ?-cell cycle regulators, apoptosis and senescence. Under the second aim, transgenic mice with condi- tional ablation of ?-cell TRPM7, which are on hand, will be utilized to assess how TRPM7 modulation of Mg2+ homeostasis regulates glucose metabolism, cAMP, Ca2+ influx and GSIS. Furthermore, the function of hu- man??-cell TRPM7 channels will be assessed with pharmacology and a dominant negative (D/N) approach, which have been established as feasible in the applicants? hands. The proposed project is significant because the resulting data will illuminate mechanistic pathways for regulating GSIS and increasing ?-cell mass; it is es- sential for uncovering therapies for treating diabetes.